Test apparatus for combustion evaluation

ABSTRACT

A combustion chamber for testing under actual burning conditions the ability of air augmented solid propellants to meet operational requirements under subsonic or supersonic environments.

United States Patent Askins et al. 1 1 Oct. 31, 1972 [54] TEST APPARATUSFOR COMBUSTION A [56] 7 References Cited EVALUATION UNITED STATESPATENTS m] :f' FR" fi 2,493,725 1/1950 McMorris ..73/3s 3,159,99712/1964 T811011 et al. ..73/35 73 Assign; Thlokd Chunk c 3,201,9738/1965 Fltzgerald et al ..73/35 Bristol, 3,225,589 12/1965 Spengler eta1. ..7 3/35 3,267,721 8/1966 Jacobs et a1. ..73/35 [22] Filed: Feb. 17,1970 Primary Examiner-Richard C. Queisser [211 App]. 12,081 AssistantExaminer-Marvin Smollar Attorney-William R. Wright, Jr. [52] U.S. Cl...73/35, 60/251, 60/254,

60/260, 60/267, 60/233, 73/167 1 ABSTRACT Int. Cl. ..G0ll A combustionchamber for testing under actual burn- [58] Field of Search ..73/35, 167ing conditions the ability of air augmented solid propellants to meetoperational requirements under subsonic or supersonic environments.

10 Claims, 15 Drawing Figures PATENTED I972 3.701. 278

sum u or 9 4 r rap/Mir PATENTED 31 I97? 3, 701 278 SHEET 5 or 9 Faber-7E. As/r/hs INVENTORS George R 905/5 A T TOP/VEV PATENTED 1973 3.701, 278

sum 7 0F 9 Faber? E. 45/0775 INVENTORS Geo/"ye Pt Pays ATTORNEYBACKGROUND OF THE INVENTION 1. Field of the Invention It became evidentin the rocket industry that there was need for equipment that couldprovide a simple relatively accurate and inexpensive procedure forscreening the specific formulations of air augmented solid propellantsunder operational requirements.

Such equipment had to be able to conduct such procedure in eithersubsonic or supersonic environments and as a result of this requirementthe testing apparatus embodying the invention was developed and hasproved entirely satisfactory in obtaining the desired information.

2. Description of the Prior Art The development of air augmentedpropulsion systems required new capabilities than those that had beenrequired normally for the development of conventional solid propellantrocket propulsion systems.

While static test facilities had been used for conventional solidpropellant rocket motors, little had been done toward testing airaugmented propulsion systems because this was a somewhat new conceptthat had been introduced into the rocket industry.

Ram-jets had been discussed, but no test facilities had been developedfor testing them, the present invention is believed, therefore, to be anew achievement in the rocket industry, because it meets a newrequirement that had not been previously established.

SUMMARY OF THE INVENTION This invention relates, therefore, to testingequipment that has the ability to test predetermined amounts of airaugmented solid propellants under actual burning conditions and topermit. such tests to be conducted under subsonic or supersonicenvironments.

There are four characteristics of subsonic or supersonic combustionwhich can be examined with the instant apparatus without introducingundue complexity:

A. Ignition or lack of ignition of the primary rocket motor exhaustproducts in the secondary chamber.

B. Under different sets of conditions the induction distance forignition in the secondary chamber may be found.

C. The pressure or temperature risealong the length of the secondarychamber may be determined.

D. The composition of the exhaust products from the secondary chamber.

It is also well-known that combustion characteristics are varied bychanges in the inlet air temperature, pressure, and velocity; along withany changes that may occur in the secondary combustion chamber section.

The apparatus-is capable, because of measured flow and temperaturecapabilities, to simulate Mach 4.0 flight at sea level, this permits theapparatus, therefore, to utilize both subsonic and supersoniccombustions.

The object of this invention, therefore, is to provide a test apparatusfor the combustion evaluation of air augmented solid propellant undersubsonic or supersonic flight conditions.

In the development of fuel-rich solid propellants for air augmentedapplications a complication is introduced by the requirement that theproducts resulting from the combustion of the solid propellant, be

capable of additional combustion with air. A factor in the earlierphases of solid propellant air augmentation development was the lack ofsufficient accurate data concerning the secondary combustion as setforth.

The instant invention was, therefore, developed to analyze the secondarycombustion that occurs with air augmented solid propellants and provideaccurate data BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a schematicview of equipment that is required for the operation of the testapparatus embodying the invention;

FIG. 2 is an elevational view of the equipment carriage that houses theair heating and control components for the test apparatus;

FIG. 3 is a sectional view of a primary motor that is positioned in thearea shown in the dotted circle 3 in FIG. 2;

FIG. 4 is a transverse sectional view on the line 4-4 of FIG. 2;

FIG. 5 is a side elevational view of the subsonic combustion componentof the test apparatus;

FIG. 6 is an elevational end view of the component of FIG. 5 taken onthe line 6-6 thereof;

FIG. 7 is a transverse sectional view taken on the line 7-7 of FIG. 5;

FIG. 8 is a diagrammatical sectional view of the venturi choke orcontrol for the air entering the primary motors of the test apparatus;

FIG. 9 is an elevational end view of the component of FIG. 5 taken onthe line 9-9 thereof;

FIG. 10 is a perspective view of the supersonic combustion component ofthe test apparatus;

FIG. 11 is a sectional view, partly in elevation, partly broken away andtaken on the line 11-11 of FIG. 10;

FIG. 12 is a longitudinal sectional view taken on the line 12-12 ofFIG.10 and line 12-12 of FIG. 15;

FIG. 13 is an elevational view, partly in section, of a wedge that isshown in dotted line position in FIG. 12;

FIG. 14 is an exploded view of one end of the com ponent of FIG. 10 andis taken on the line 14-14 of FIG. 12; and

FIG. 15 is an elevational view of another end of the component of FIG.10 and is taken on the line 15-15 of FIG. 12.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring more in detail to thedrawings wherein like parts are designated by like reference numeralsand more especially to FIG. 1 wherein the reference numeral 20 is usedto designate a facility which includes the various pieces of equipmentthat are necessary for the operation of the test apparatus embodying theinvention.

The facility 20 includes a compressed air supply storage tank 21 whichis connected by suitable conduits to a pop-safety relief valve 22 and togate valves 23, 24, 25 and 26 all of which control the flow of air underpressure from the tank 21. A pressure gauge 27 is also connected by thesuitable conduits to indicate the air pressure within the tank 21. Aflexible supply conduit 28,. having suitable couplings 29 on theopposite ends thereof, provide means whereby compressed air may besupplied to the tank 21.

An air supply conduit 30 is connected to the gate valve 24 and thenextends to a gate valve 31 and then to be connected to a flexibleconduit 32 by a coupling 33. The flexible conduit 32, by means of acoupling 34, is connected to a conduit 35 which will be connected to thetest apparatus as will be later described.

Another conduit 36 is suitably connected to the air supply conduit 30and extends to a regulator 37 which in turn is connected to a gate valve39 by a conduit 38 which is connected by a coupling 40 to a flexibleconduit 41 that is connected by a coupling 42 that is also connected toa conduit 43 which will be connected to the test apparatus as will belater described.

The conduit 38 is suitably connected to a conduit 44 that is connectedto a test gauge 45 and a conduit 46 connects the conduit 36 directly toa second test gauge 47.

A third test gauge 48 is connected by a conduit 49 to a gate valve 50which is then connected by a coupling 51 to a flexible conduit 52 whichby a coupling 53 is connected to a conduit 54 that is connected to thetest apparatus depending on the tests that are being conducted.

A selector switch 55 is connected by a line 56 to a receptacle 57 whichin turn is connected by line 58 to a receptacle 59 that is connected tothe test apparatus as will be later described. As shown the test gauges45, 47 and 48, regulator 37 and selector switch 55 are all mounted on apanel 60 for convenience and observation during the testing periods.

As shown by dotted lines in FIG. 1 and more specifically in FIG. 2, thetest apparatus comprises what is termed an equipment carriage 61 thatincludes a boxlike body 62 that has a cavity 63 at one end thereof andis provided for the sake of mobility with dolly wheels 64. Mounted onthe exterior surface of one side of the body 62 is a conventional safetyswitch 65 to which is connected an electric cable 66 that is connectedto an electrical power source. Mounted adjacent the safety switch 65 isan electrical control 67 and adjacent that is mounted an indicatingon-off device 68 for the control 67 and all three are connected togetherby a cable 69. While the indicating device 68 is connected by a line 70to a thermocouple 71 and the control 67 has an electrical cable 72connected thereto.

Viewing FIGS. 2 and 4, it will be seen that the body 62 is lined'withslabs of insulation 73 which are positioned to leave a longitudinallyextending chamber or cavity 74 within and surrounded by the insulation73, it will also be noted that the thermocouple 71 extends into thechamber 74. The conduit 35 (FIG. 1) is connected to an inlet box 75 towhich is connected a conduit 76 that is connected to a regulator 77 andextending from the regulator 77 into the chamber 74 in the body 62 is aconduit 78 that within the chamber 74 is formed into a coil 79 which issupported by one or more brackets 80. Extending throughthe chamber 74longitudinally thereof and resting on the insulation 73 are electricalheating elements 81 'which by conductors 82 are connected to the cable72 within a junction box 83 that is mounted on the bottom of the body62.

Extending from the coil 79 is a conduit 84 that is connected to aventuri choke or control 85 (see FIG. 8) that comprises a pair ofapertured disks 86 and 87, the disk 86 being connected to a conduit 88and the disk 87 being connected to the conduit 84. Positioned betweenthe disks 86 and 87 is a circular block 89 the center of which iscontoured as at 90 to resemble a divergentconvergent nozzle which isalined with the conduits 84 and 88. Fasteners 91 secure the disks 86 and87 in position as shown in FIG. 8 and circular gaskets 92 and 93 mountedin the inner surfaces of the disks 86 and 87 seal the block 89 toprevent leakage of air therefrom.

The conduit 88 extends to a cylindrical plenum chamber 94 at the endthereof which is mounted in relation to the equipment carriage 61 asshown in FIG. 2 and a small rocket motor 95 is connected to the head endof the plenum chamber 94 as shown in FIG. 3, and the conduit 88 betweenthe body 62 and the plenum chamber 94 is covered with insulation 96.Unions 97 may be interpolated in conduits 76 and 78 for removal of theregulator 77 as desired and a secondary source of air under pressure isfed to the equipment carriage 61 by a flexible conduit 97 that isconnected to an electrically operated valve 98 that is connected to andcontrols the flow of air from the inlet box 75. The conduit 43 isconnected to the regulator 77 and a line 99 extends from the receptacle59 to the valve 98 all as shown in FIG. 1.

The plenum chamber 94 has a liner sleeve 100 positioned therein that isprovided with an opening 101 to receive the end of the conduit 88 thatextends through an opening 102 in the plenum chamber 94 whereby theconduit 88 is in communication with the plenum chamber 94. Directlyopposite to the opening 101 the sleeve 100 is provided with a secondopening 103 which communicates with a circular cavity 104 that is alinedwith an internally threaded bore 105 that receives a coupling 106whereby the plenum chamber 94 is connected to the conduit 54. The plenumchamber 94 is rigidly mounted on the top of the equipment carriage 61 bymeans of an L-shaped bracket 107 and the head end of the plenum chamber94 is provided with a circular row of internally threaded bores 108whereby an annular flange 109 at the aft end of a motor case 110 for therocket motor 95 is connected to the head end of the plenum chamber 94 bybolts (not shown) that will extend through-countersunk internallythreaded bores 111 in the flange 109 into the bores 108 in the head endof the plenum chamber 94 when such bores are in alinement with eachother. The motor case 110 is provided with an internally threaded boss112 which receives an ignition 113, and a second annular flange 114 onthe head end of the motor case 110 is removably secured by anywell-known means to a closure plate 115 for the motor case 110. Duringthe operation of the test apparatus, a disk-shaped charge of a solidpropellant grain A will be positioned in the head end of the motor case110 in contact with the closure plate 115 as shown in FIG. 3 and as willbe later described. The aft end of the motor case 110 within the flange109 has positioned therein a circular inverted nozzle 116 and the headend of the liner 100 engages an annular shoulder 117 in the periphery ofthe nozzle 116 to retain it in position in the motor case 110 as shownin H6. 3 so that the nozzle 116 is in communication with the plenumchamber 94.

The aft end of the plenum chamber 94 is also provided with a circularrow of internally threaded bores 118 whereby a plate 119 correspondingin size to the peripheral area of the plenum chamber 94 is securedthereto by bolts 120 that will extend through countersunk bores 121 inthe plate 119 into the bores 118 when such bores are in alinement witheach other.

The side edges of the plate 119 are provided with a plurality of equallyspaced cutouts 122 that form therebetween a plurality of projections 123each of which are provided with a centrally located aperture for apurpose to be later described.

The projections 123 on the plate 119 are received in equally spacedcutouts 124 at the aft end of a sub-sonic secondary combustion chamber125 that at times is referred to as a nozzle by personnel performing thetest. A plurality of projections 126 are formed at the aft end of thecombustion chamber 125 by the cutouts 124 and each of the projections126 are provided with a centrally located aperture so that when theseapertures are alined with the apertures in the projections 123 latchingpins 127 are sled into the alined projections to removably secure thecombustion chamber 125 to the plate 119.

The plate 119 is provided with a centrally located opening 128 and anannular flange 129 on the plate 119 surrounds the opening 128 on theinside of the plate 119 and a groove 130 is provided on the exteriorsurface of the flange 129 to receive a gasket 131 that provides a leakproof connection between the plate 119 and an annular cutout 132 at theaft end of the combustion chamber 125 in which the flange 129 is seated.

The opening 128 in the plate 119 is alined with a longitudinallyextending centrally located circular chamber 133 in the combustionchamber 125 and a liner sleeve 134 positioned in the chamber 133 abutsat the head end thereof with the aft end of the liner sleeve 100 in theplenum chamber 94 and the exterior surface of the sleeve 134 is providedwith a plurality of relatively spaced feet 135, FIG. 5, to space thesleeve 134 from the insurface of the chamber 133 to provide alongitudinally extending circular gap B therebetween.

The opposite sides of the combustion chamber 125 are each provided witha longitudinally extending row of partially internally threaded openings136 into each of which is threaded a partially externally threadedviewing port 137 in each of which is mounted a sight glass 138. Gaskets139 and 140 at opposite ends of the sight glass 138 provide a leak proofassembly. Each of t the openings 136 communicate with the gap B in theThe aft end of the combustion chamber is provided with a circular row ofinternally threaded bores 146 whereby a plate 147 of the same peripheralsize as the combustion chamber 125 is secured to the aft end of thecombustion chamber 125 by bolts 148 that extend through internallythreaded bores 149 in the plate 147 into the bores 146 in the aft end ofthe combustion chamber 125.

The plate 147 is provided with a centrally located partially threadedopening 150 in which is positioned a nozzle 151 and an externallythreaded retaining ring 152 threaded into the opening 150 and engagingan annular ridge 153 on the periphery of the nozzle 151 serves to retainthe nozzle 151 in position in the plate 147 and the combustion chamber125 is mounted on the carriage 61 by means of a pair of L-shapedbrackets 154 and 155.

In FIGS. 10 to 15 inclusive, there is shown a supersonic secondarycombustion chamber 156 which for certain tests will replace the subsonicsecondary combustion chamber 125 as will be later described.

The combustion chamber 156 comprises two parts 157 and 158 that havevertically disposed mating edges 159 and 160 that are nested in verticalrelation to each other as shown in FIGS. 14 and 15. Each of the parts157 and 158 have a longitudinal row of openings 16] at the bottom ofpart 157 and at the top of part 158 to receive suitable bolts wherebythe parts 157 and 158 may be nested together and retained in thisposition as shown in FIG. 10. Each of the parts 157 and 158 have viewingports 162 provided therein which are retained in place by bolts 163.

The part 157 has an opening 164 therein adjacent one of the viewingports 162 through which a pressure tap 165 extends and the aft end ofthe parts 157 and 158 are provided with a plurality of internallythreaded bores 166.

The plenum chamber 94 in these Figures is basically the same aspreviously described, except that the plate 119 is replaced by acircular plate 167 which has a central opening 168 therein and issecured the plenum chamber by bolts 169 entering the bores 118 throughopenings 170 in the plate 167, a conduit 171 has one end thereofinserted into the opening 168 and is rigidly secured to the plate 167 bywelding 172 as shown in FIG. 10. The conduit 171 at its aft end abutsthe sleeve 100 in the plenum chamber 94 and at the head end thereofenters the central opening 173 of a plate 174 which is secured to thecombustion chamber 156 by bolts 175 entering the bores 166 throughopenings 176 in the plate 173.

In these Figures the rocket motor 95 is eliminated and a closure plate177 is secured to the plenum chamber 94 by bolts 178 entering the bores108 in the plenum chamber through the openings 179 in the closure plate177.

In the use of the combustion chamber 156 the rocket motor 180 is mountedon the top thereof and comprises an aft end 181, a central case portion182 and a head end closure 183. The aft end 181 is connected to the part157 of the combustion chamber 156 by an externally threaded boss 184that enters the internally threaded bore 185 in the part 157 and the aftend 181 has a throat portion 186 that communicates with a nozzle 187that is positioned in an opening 188 in the part 157. The head end ofthe aft end 181 is welded at 189 within the combustion chamber 190 inthe case portion 182 which is provided with blow out plugs or ports 191and has an internally threaded bore 192 to receive a thermo-couple 193having an electric feed line 194 and an internally threaded bore 195 isprovided to receive an igniter 196 that is provided with plus and minuselectric feed lines 197 and 198..

The case portion 182 is provided with an internally threaded annularflange 199 into which is threaded a reduced externally threadedprojection 200 on the head end 183 which is provided with a cavity 201that is lined with insulation 202 and 203 and a solid propellant 204having a liner 205 thereon is positioned within the head end 183 asshown in FIG. 12.

The combustion chamber 156 has a chamber 206 therein which is formed byvertical side surfaces 207 in each of the parts 157 and 158, horizontaltop surfaces 208 in each of the parts 157 and 158 and convergent orupwardly inclined bottom surfaces 209 in each of the parts 157 and 158.The side surfaces 207, top surfaces 208 and bottom surfaces 209 allconverge inwards to a nozzle throat area 210 and as shown in FIG. 12,the discharge of the nozzle 187 of the combustion products formed by theburning of the solid propellant 204 communicate with the discharge ofair from the nozzle throat area 210 and an Oring 211 seals the areaabout the nozzle 187 as shown in FIG. 12.

The volume of the chamber 206 may be altered by mounting wedges 212 asshown in FIG. 13 by inserting bolts 213 through spaced opening 214 inthe top of the part 157 to be received in internally threaded bores 215in the wedges 212.

The part 158 is also provided with a plurality of inlets 216 which servethe same purpose as the inlets 144 as will be later described.

It is a well-known fact that air augmentedpropulsion systems involve theburning of a solid propellant grain in a primary combustion chamberexhausting the combustion products from the chamber into a secondarycombustion chamber in which air is mixed with the combustion productsand the combined mixture is exhausted through a nozzle to provide thedesired thrust. A typical rocket motor of this type being exemplified inUS. Pat. No. 3,173,249.

In order, therefore, to determine the characteristics displayed bycertain types of solid propellant grains, there was a need for a testapparatus that could exactly duplicate the operation of an air augmentedpropulsion system in flight and the instant test apparatus was sodesigned and operates in the following manner.

It may be said that the basic component of the test apparatus is theequipment carriage 61 shown in FIG. 2

The schematic of FIG. 1 depicts the system whereby air under pressure isfed to the equipment carriage 61 so that such air under pressure, aspreviously stated, may be fed to a secondary combustion chamber toduplicate the flight operation of an air augmented propulsion system.

In FIG. 2 it is shown how the air under pressure, as is supplied by thearrangement of the component of FIG. 1, is fed to the equipment carriage61 by means of the conduit 35 and the description of FIG. 2 explains howthe air is heated and then fed to the plenum chamber 94 under controlledvelocity, pressure and temperature.

If the test is to be conducted for subsonic conditions, the secondarycombustion chamber of FIGS. 5, 6 and 7 is connected to the plenumchamber 94 as described for FIGS. 3, 5, 6 and 7. A propellant sample Ais ignited in a small rocket motor 95 which is connected to the plenumchamber 94 as previously described and the combustion products createdby the burning of the sample A exhausts through the nozzle 116 into theplenum chamber 94 where it is mixed with the controlled air entering theplenum chamber 94 through the conduit 88 after it has been heated by thecoil 79 in the equipment carriage 61, as previously described.

The combination of heated air and combustion products is then fed intothe secondary combustion chamber 125. The mixture in the combustionchamber 125, because of the pressure and heat created by the heated air,will burn and such burning can be viewed through ports 137. Testequipment for pressure, temperature and velocity determinations may beconnected to selected ports 144 and such equipment is determined by theoperator conducting such tests.

Nitrogen may also be introducted into the the combustion chamber topurge the chamber 125 and thus increase the efficiency of the test. Itwill be understood that the mixture of combustion products and air inthe chamber 125 will exhaust through the nozzle 151 and nozzles ofvarious configurations and sizes may be used to change the ratio ofthrust that is created by the burning of the products within thecombustion chamber 125. This test is conducted at subsonic rates only.

If supersonic tests are to be conducted the secondary combustion chamber156 of FIGS. 10to 15 inclusive is used and basically the test is thesame, except that the rocket motor is mounted on top of the secondarycombustion chamber 156 and the plenum chamber 94 is connected to thechamber 156 as shown in .FIG. 1 I.

As shown in FIGS. 10 and 12 the solid propellant grain 204 is ignitedand combustion products formed by the burning thereof is exhaustedthrough nozzle 187 into an air stream that is passing through nozzle 210and the mixture thus created is forced by the generated pressure ofcombustion products and air pressure into the combustion chamber 156.The air stream coming from the plenum chamber 94 through conduit 171will be travelling at supersonic velocity when it mixes with thecombustion products. The results of the mixing of the combustionproducts and pressurized air may be viewed through ports 162 and thechanging of various sizes of wedges 212 as shown in FIGS. 12 and 13 andselected instrumentations may be used to determine temperature, pressureand velocity within the combustion chamber 156.

Thus basically the test is the same whether or not the .subsonic or thesupersonic secondary combustion vides an excellent means for low costsolid propellant grain screening for air augmented propulsion systems.

It is believed also that from a study of the foregoing description theinvention will be clear to one skilled in the art and it is to beunderstood that variations in the structure described and the methods ofuse of such structure may be adhered to provided such variations fallwithin the spirit of the invention and the scope of the appended claims.

Having thus described the invention what is claimed as new and desiredto be secured by Letters Patent is:

l. A test apparatus for the combustion evaluation of air augmented solidpropellant grains comprising a carriage, means for supplying air underpressure to said carriage, said carriage having means thereon forheating said air under pressure, a secondary combustion chamber mountedon said carriage, a plenum chamber connected to the means for supplyingair and in communication with said secondary combustion chamber, aprimary rocket motor in communication with said secondary combustionchamber having a sample of an air augmented solid propellant graintherein which when ignited will cause combustion products created by theburning thereof to be mixed with the air under pressure in saidsecondary combustion chamber.

2. A test apparatus as in claim 1 wherein the air under pressure is fedto said secondary combustion chamber at subsonic velocity. k 3. A testapparatus as in claim 1 wherein air under pressure is fed to saidsecondary combustion chamber at supersonic velocity.

4. A test apparatus as in claim 1 wherein said primary rocket motor ismounted on the upper surface of said secondary combustion chamber.

5. A test apparatus as in claim 1 wherein said primary rocket motor ismounted on said plenum chamber in communication therewith.

6. A test apparatus as in claim 1 wherein wedges are mounted in saidsecondary combustion chamber to control the velocity of the combustionproducts and air under pressure.

7. A test apparatus as in claim 1 wherein viewing ports are provided insaid secondary combustion chamber.

8. A test apparatus as in claim 1 wherein igniter means is provided forigniting the air augmented solid propellant grain in said primary rocketmotor.

9. A test apparatus as in claim 1 wherein the chamber in said secondarycombustion chamber is formed by a longitudinally extending tubularmember.

10. A test apparatus as in claim 1 wherein the chamber in said secondarycombustion chamber has vertical sidewalls, a horizontal upper wall andan inwardly inclined bottom wall that all converge toward a nozzle areaat the head end of said secondary combustion chamber.

1. A test apparatus for the combustion evaluation of air augmented solidpropellant grains comprising a carriage, means for supplying air underpressure to said carriage, said carriage having means thereon forheating said air under pressure, a secondary combustion chamber mountedon said carriage, a plenum chamber connected to the means for supplyingair and in communication with said secondary combustion chamber, aprImary rocket motor in communication with said secondary combustionchamber having a sample of an air augmented solid propellant graintherein which when ignited will cause combustion products created by theburning thereof to be mixed with the air under pressure in saidsecondary combustion chamber.
 2. A test apparatus as in claim 1 whereinthe air under pressure is fed to said secondary combustion chamber atsubsonic velocity.
 3. A test apparatus as in claim 1 wherein air underpressure is fed to said secondary combustion chamber at supersonicvelocity.
 4. A test apparatus as in claim 1 wherein said primary rocketmotor is mounted on the upper surface of said secondary combustionchamber.
 5. A test apparatus as in claim 1 wherein said primary rocketmotor is mounted on said plenum chamber in communication therewith.
 6. Atest apparatus as in claim 1 wherein wedges are mounted in saidsecondary combustion chamber to control the velocity of the combustionproducts and air under pressure.
 7. A test apparatus as in claim 1wherein viewing ports are provided in said secondary combustion chamber.8. A test apparatus as in claim 1 wherein igniter means is provided forigniting the air augmented solid propellant grain in said primary rocketmotor.
 9. A test apparatus as in claim 1 wherein the chamber in saidsecondary combustion chamber is formed by a longitudinally extendingtubular member.
 10. A test apparatus as in claim 1 wherein the chamberin said secondary combustion chamber has vertical sidewalls, ahorizontal upper wall and an inwardly inclined bottom wall that allconverge toward a nozzle area at the head end of said secondarycombustion chamber.